1. Field of the Invention
The present invention relates to an optical panel for use in a flashing device, and more particularly to an optical panel for a flashing device employing a flashing system wherein a hat-like reflector condenses light emitted from a flashing discharge tube and illuminates a photographic object, as well as controlling light distribution characteristics.
2. Related Background Art
Flashing devices which condense light from a flashing discharge tube and illuminate a photographic object have heretofore been proposed and generally put into practical use. For example, a conventional flashing device as shown in FIG. 7 is made up of a flashing discharge tube 101 and a reflector 102 and provides an illuminating angle made between a line connecting the center of the flashing discharge tube 101 with an upper end portion of the reflector 102 and a line connecting the center of the flashing discharge tube 101 with a lower end portion thereof, i.e., defined by a diverging angle .theta.10 of direct light 108 from the flashing discharge tube.
On the other hand, various flashing devices have also been put in practical use, wherein an optical panel or the like is disposed in front of the flashing discharge tube and reflector to control light distribution characteristics for the purpose of converging the light from the flashing discharge tube within a desired illuminating angle.
For instance, in an optical panel for a flashing device as disclosed in Japanese Laid-Open Utility Model No.145030 of 1981, first control structures having an excellent light distribution characteristic at a circumferential portion of a reflector are arranged in front of and at both sides of the reflector with respect to its longitudinal direction and a second control structure having a great light distribution characteristic at a central portion of the reflector is placed at a central portion between the first control structures so that different light distribution characteristics are provided for the central portion and circumferential portion. This arrangement can converge light, directed at a circumferential portion of a photographic object along a longitudinal direction of the reflector, to a central portion thereof.
In addition, a flashing device, as disclosed in Japanese Laid-Open Patent Application No. 138438 of 1992, is equipped with a prism having a positive refractive surface, an incident surface for receiving light advancing toward side-way portions of a light-emitting source (flashing discharge tube), a total reflection surface for total-reflection of the light incident on the reflection surface, and an emission surface for forwardly emitting the light total-reflected by the total reflection surface. In addition, at different areas the flashing device is attendant with an emission opening for the direct light advancing forwardly without passing through the prism and another emission opening for the reflected light proceeding forwardly through the prism. According to this flashing device, divergent light, emitted from the light-emitting source (flashing discharge tube) but not directly reaching a photographic object, passes through the prism, thereby being converged into an illuminating angle.
However, in such a general flashing device as shown in FIG. 7 the illuminating angle .theta.10 of the direct light 108 is capable of covering a photographing angle of view when the reflector 102 is large in size, while, with the flashing device itself being reduced in size, a reflector 102a thereof is also reduced in size as illustrated in FIG. 8, whereby an illuminating angle .theta.10a thus obtained becomes wide so that direct light 108a from a flashing discharge tube 101a is widely diffused to result in an illumination range exceeding the photographing angle of view. Accordingly, a problem exists in that illumination light loss will occur by reason of the light diffusion from the flashing discharge tube 101a.
Therefore, as illustrated in FIG. 9, an optical panel 103 whose inner surface has a convex configuration may be placed in front of a flashing discharge tube and reflector so as to refract light directly advancing to a photographic object for the control of the illumination light loss. In this case, direct light 108b from a flashing discharge tube 101b is adapted to be refracted through the optical panel 103 so as to be directed at within the illuminating angle with improved convergent performance. On the contrary, light reflected on a reflector 102b results in being refracted through the optical panel 103 before proceeding out of the photographing angle of view (light 106), whereby difficulty is encountered to efficiently lead the light from the flashing discharge tube 101b into the photographing angle of view, thus producing illumination light loss.
On the other hand, when as shown in FIG. 10 a plate-like optical panel is disposed in front of a flashing discharge tube and reflector, the light 106a emitted from the flashing discharge tube 101c before reflected on the reflector 102c is refracted through the optical panel 103c so as to advance into the photographing angle of view, while illumination is made such that direct light 108c from the flashing discharge tube 101c is refracted out of the photographing angle of view by means of the optical panel 103c. This causes illumination light loss.
For these reasons, there is a problem which arises with small-size flashing devices having the optical panels 103, 103c as shown in FIGS. 9 and 10, in that difficulty is experienced in simultaneously controlling the direct light 108b, 108c and reflected light 106, 106a.
Moreover, for the purpose of size-reduction of a flashing device as shown in FIG. 11 wherein a reflector 102d is set so that the angle .theta.11 of direct light from a flashing discharge tube 101d and the angle .theta.12 of reflected light therefrom provide illumination within a photographing angle of view .theta.13, that is, in a case where reflector 102d shown in FIG. 11 is arranged to be shortened in depth as a reflector 102e as shown in FIG. 12 and the reflector 102e is disposed so that the angle .theta.12a of reflected light is less than an illuminating angle .theta.13a, the angle .theta.11a of the outermost portion of direct light from a flashing discharge tube 101e becomes considerably wider than a desired illuminating angle .theta.13a. Thus, this creates a problem in that illumination light loss is developed in an area L indicated with oblique lines in FIG. 12.
In other words, when as illustrated in FIG. 13 an illuminating angle .theta.101b made between a line connecting the center of a flashing discharge tube 101f with an upper end portion of a reflector 102f and a line connecting the center of the flashing discharge tube 101 with a lower end portion thereof is larger than a desired illuminating angle .theta.103b, the loss of illumination light will occur.
Furthermore, according to the means disclosed in the Japanese Laid-Open Utility Model No. 145030 of 1981, a problem also exists in that said means provides only the control of light distribution in a longitudinal direction of the reflector, but does not provide effective utilization of illuminating light in a transverse direction of the reflector.
Additionally, according to the means disclosed in the Japanese Laid-Open Patent Application No. 138438 of 1992, a problem also exists in that the frontage of the reflector becomes large because of placing a prism at its circumferential portion.